The life cycle of a fly includes an egg, larva, pupa and adult. A fly completes its life cycle in 1 week to 2 months, depending on environmental conditions.
The egg of the housefly is tiny and white. Over a 3- to 4-day period, a female fly lays as many as 500 eggs, with larger females producing more eggs. Females produce eggs best at temperatures between 77 and 86 degrees Fahrenheit. Housefly eggs require a moist environment to hatch.
Eggs hatch in 8 to 20 hours, and the larva feeds upon its substrate. Fly larvae, or maggots, are soft, legless and white. The larvae go through three instars, or stages, before becoming ready to form a pupa. Under the best conditions, larvae are ready to move on to the next life stage within 4 to 13 days.
During the pupal stage, maggots form a case from their skin; the pupa changes from white through shades of red and brown, and finally to black as it ages. Pupal development requires 2 to 6 days under good conditions. After the requisite time passes, the fly uses a special inflatable sac in its head to break open the pupa.
The adult fly is gray to yellow in color, with red eyes. Female flies are larger than males, with more space between their eyes. The adult fly lives approximately 2 weeks to 2 months.